锆合金变形机理及其板材织构演化规律

锆是核工业的重要结构材料,又是优秀的化工耐蚀结构材料。锆合金的织构会对它的屈服强度、蠕变和疲劳强度、应力腐蚀开裂行为以及辐照尺寸变化等产生很大影响,因此变形机理的研究和织构控制在锆合金的开发利用中有十分重要的地位。综述了锆合金的变形机理,介绍了锆合金板材在不同轧制温度下的织构演化规律,以及退火温度对锆合金板材织构的影响,并总结了织构对锆合金板材力学性能的影响。最后指出,目前对锆合金板材加工后的织构进行精确预测还十分困难,需进行详细深入的研究,同时在加工中产生的织构对加_丁过程的影响以及与温度、应力分布、合金成分和组织的关系还需进一步认识。     

锆合金变形机理及其板材织构演化规律

锆是核工业的重要结构材料,又是优秀的化工耐蚀结构材料.锆合金的织构会对它的屈服强度、蠕变和疲劳强度、应力腐蚀开裂行为以及辐照尺寸变化等产生很大影响,因此变形机理的研究和织构控制在锆合金的开发利用中有十分重要的地位.综述了锆合金的变形机理,介绍了锆合金板材在不同轧制温度下的织构演化规律,以及退火温度对锆合金板材织构的影响,并总结了织构对锆合金板材力学性能的影响.最后指出,目前对锆合金板材加工后的织构进行精确预测还十分困难,需进行详细深入的研究,同时在加工中产生的织构对加工过程的影响以及与温度、应力分布、合金成分和组织的关系还需进一步认识.     

Kinetic Pathways of Phase Transformations in Two-Phase Ti Alloys

Possible phase transformation kinetic pathways from the high temperature β phase to the low temperature (α + β) two-phase Ti alloys were analyzed using the graphical thermodynamic method and the assumption that diffusionless and displacive transformations take place much faster than phase separation which requires long-range diffusion. It is shown that depending on the composition of a β-stabilizing element, many transformation mechanisms are possible, involving competing continuous and discontinuous displacive/diffusional transformations. We discuss the proposed phase transformation sequences employing existing experimental microstructures.     

Phase Transition and Texture Evolution in the Ni-Mn-Ga Ferromagnetic Shape-Memory Alloys Studied by a Neutron Diffraction Technique

The phase transition and influence of the applied stress on the texture evolution in the as-cast Ni-Mn-Ga ferromagnetic shape-memory alloys were studied by the time-of-flight (TOF) neutron diffraction technique. The neutron diffraction experiments were performed on the General Purpose Powder Diffractometer (Argonne National Laboratory). Inverse pole figures were determined from the neutron data for characterizing the orientation distributions and variant selections of polycrystalline Ni-Mn-Ga alloys subjected to different uniaxial compression deformations. Texture analyses reveal that the initial texture for the parent phase in the as-cast specimen was composed of , , , and , which was weakened after the compression deformation. Moreover, a strong preferred selection of martensitic-twin variants (and ) was observed in the transformed martensite after a compression stress applied on the parent phase along the cyclindrical axis of the specimens. The preferred selection of variants can be well explained by considering the grain/variant-orientation-dependent Bain-distortion energy. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.     

Effect of Strain Rate on Evolution of the Deformation Microstructure and Texture in Polycrystalline Copper and Nickel

The evolution of crystallographic texture in polycrystalline copper and nickel has been studied. The deformation texture evolution in these two materials over seven orders of magnitude of strain rate from 3 × 10⁻⁴ to ~2.0 × 10⁺³ s⁻¹ show little dependence on the stacking fault energy (SFE) and the amount of deformation. Higher strain rate deformation in nickel leads to weaker á 101 ñ \left\langle {101} \right\rangle texture because of extensive microband formation and grain fragmentation. This behavior, in turn, causes less plastic spin and hence retards texture evolution. Copper maintains the stable end á 101 ñ \left\langle {101} \right\rangle component over large strain rates (from 3 × 10⁻⁴ to 10⁺² s⁻¹) because of its higher strain-hardening rate that resists formation of deformation heterogeneities. At higher strain rates of the order of 2 × 10⁺³ s⁻¹, the adiabatic temperature rise assists in continuous dynamic recrystallization that leads to an increase in the volume fraction of the á 101 ñ \left\langle {101} \right\rangle component. Thus, strain-hardening behavior plays a significant role in the texture evolution of face-centered cubic materials. In addition, factors governing the onset of restoration mechanisms like purity and melting point govern texture evolution at high strain rates. SFE may play a secondary role by governing the propensity of cross slip that in turn helps in the activation of restoration processes.     

TiAl合金中的TiB2相生长形态及其对力学性能的影响

研究了B含量分别为0.2％和1.0％(原子分数)两种TiAl合金中TiB2相的生长机制,结果表明G2(Ti-47.5Al-5( Cr,Nb,W,Si)+1.0B％)合金中少量TiB2相是由于成分起伏从液相中生成的初生块状TiB2相,大部分TiB2相是在凝固过程与β相共同耦合生长的次生带状、杆状TiB2相;G1( Ti-47.5Al-5( Cr,Nb,W,Si)+0.2B％)合金中TiB2相是由共晶反应生成的次生带状TiB2相.G2合金全片层组织和网篮组织室温塑性均优于G1合金,网篮组织室温强度与Gt合金相当,而全片层组织室温强度却不如G1合金.在760 ℃/100 MPa/200 h蠕变条件下G2合金全片层组织残余蠕变量和蠕变速率均低于G1合金.     

Influence of Strain Rate Sensitivity on Cube Texture Evolution in Aluminium Alloys

The influence of strain rate sensitivity on development of Cube texture and on the morphology of Cube-oriented grains is often neglected in simulations approaches. Therefore, crystal plasticity simulations and experiments were performed up to 73 pct of thickness reduction for cold rolling on Al 6016. It is found, that low values of strain rate sensitivity promote Cube grains fragmentation and avoid formation of transition bands already at 50 to 55 pct thickness reduction. High values of strain-rate sensitivity cause formation of Cube transition bands leaving thin Cube grains in the microstructure and delay their fragmentation. Other texture components are affected by changes in strain rate sensitivity as well. The Copper volume fraction in the final texture diminishes as the strain rate sensitivity decreases, while Brass and S components of the beta fiber show a moderately higher volume fraction when the strain rate sensitivity increases. The final volume fraction of Goss is highest when the strain rate sensitivity is 10⁻² but low if the strain rate sensitivity is 10⁻³ or raises up to 10⁻¹. Recrystallization texture components (P, Q) are not affected by strain rate sensitivity, while the invGoss fraction decreases for high values of strain rate sensitivity. The results found in cold rolling crystal plasticity simulations were compared with experimentally determined Cube distribution and texture components obtained through thickness for Al6016 rolled at 80 m/min and 600 m/min. Further crystal plasticity simulations were performed to predict the influence of strain rate sensitivity during several hot rolling conditions where activity of non-octahedral slip systems was included in the simulations. During hot rolling, high values of strain rate sensitivity contribute to Cube stabilization and promote formation of Copper texture and delay Brass and S.

     

Aging Effect on Texture Evolution during Warm Rolling of ZK60 Alloys Fabricated by Twin-Roll Casting

ZK60(Mg-Zn-Zr) alloys experience variation of precipitates during aging. The frequency and size of rod- and disk-shaped precipitates change with aging. The effect of aging on texture evolution during warm rolling of ZK60 was investigated. Some difference was found between the texture evolution of solution heat-treated (T4) and artificially aged (T6) samples. The Aged samples had more texture variations along the thickness direction than solution heat-treated samples. The intensities of basal fibers were lower during asymmetric rolling than during symmetric rolling, although the initial intensities increased during both rolling processes. The decrease in basal fibers by asymmetric rolling was clearer at a lower temperature of 448 K (175 °C) than at 498 K (225 °C).     

Effect of Tungsten Content and Compression on Microstructure and Texture Evolution in Liquid Phase Sintered Heavy Alloy

Metallurgical and Materials Transactions A - The crystallographic texture development in uniaxial compression tests of tungsten heavy alloys was systematically investigated by varying the tungsten...     

Role of Solute in the Texture Modification During Hot Deformation of Mg-Rare Earth Alloys

Although conventional Mg alloys develop strong crystallographic textures during deformation that persist during annealing, the addition of rare earth (RE) elements can induce comparably weaker textures. The texture weakening effect is explored using hot-rolled Mg-Y alloys of a single phase to focus on the possibility of solute effects. Of the studied compositions, the richer alloys (≥0.17 at. pct) show the weakening effect, whereas the most dilute alloy (≤0.03 at. pct) does not. Electron backscattered diffraction (EBSD) analysis of intragranular misorientation axes (IGMA) indicate that the geometrically necessary dislocation (GND) content in dilute, hot-rolled alloys contain primarily basal 〈a〉 dislocations. At higher concentrations, the dislocations are predominantly prismatic 〈a〉 type. This change in the GND content suggests a change in dynamic recrystallization (DRX) mode. For example, nonbasal cross slip has been associated with continuous DRX. Furthermore, nonbasal slip might also promote more homogenous shear banding/twinning. Both of these mechanisms have been shown previously to give rise to more randomly oriented nuclei during DRX. Energy dispersive X-ray spectroscopy performed through transmission electron microscopy shows that Mg-Y exhibits significant grain boundary solute segregation, consistent with recent observations of solute clustering. Slow grain growth may be explained by solute drag. It is hypothesized that limited grain boundary mobility suppresses conventional discontinuous DRX, which has been shown to retain the deformation texture. The promotion of nonbasal slip and suppression of grain boundary mobility are proposed as solid solution-based mechanisms responsible for the observed texture weakening phenomenon in Mg rare earth alloys.     

Evolution of Constitution,Structure, and Morphology in FeCo-Based Multicomponent Alloys

Constituent phases, melting behaviors, and microstructure of multicomponent (Fe_0.5Co_0.5) _x (Mo_0.1C_0.2B_0.5Si_0.2)_100–x alloys (x = 95, 90, 85, 80, and 70) produced by copper mold casting were evaluated by various analysis techniques, i.e., X-ray diffractometry, scanning electronic microscopy with energy dispersive X-ray spectrometry, and differential scanning calorimetry. Metastable Fe₃C- and Cr₂₃C₆-type phases were identified in the chill-cast alloys. A schematic illustration was proposed to explain the evolution of constituent phases and microstructure for the alloys with x = 95, 90, and 85 during the solidification process, which could be applicable to controlling microstructural formation of other multicomponent alloys with similar microstructures by artificially adjusting the composition.     

Effect of Thermomechanical Processing on Microstructure,Texture Evolution,and Mechanical Properties of Al-Mg-Si-Cu Alloys with Different Zn Contents

The effect of thermomechanical processing on microstructure, texture evolution, and mechanical properties of Al-Mg-Si-Cu alloys with different Zn contents was studied by mechanical properties, microstructure, and texture characterization in the present study. The results show that thermomechanical processing has a significant influence on the evolution of microstructure and texture and on the final mechanical properties, independently of Zn contents. Compared with the T4P-treated (first preaged at 353 K (80 °C) for 12 hours and then naturally aged for 14 days) sheets with high final cold rolling reduction, the T4P-treated sheets with low final cold rolling reduction possess almost identical strength and elongation and higher average r values. Compared with the intermediate annealed sheets with high final cold rolling reduction, the intermediate annealed sheets with low final cold rolling reduction contain a higher number of particles with a smaller size. After solution treatment, in contrast to the sheets with high final cold rolling reduction, the sheets with low final cold rolling reduction possess finer grain structure and tend to form a weaker recrystallization texture. The recrystallization texture may be affected by particle distribution, grain size, and final cold rolling texture. Finally, the visco-plastic self-consistent (VPSC) model was used to predict r values.

     

Phase Structure and High-Temperature Mechanical Properties of Two-Phase Fe-25Al-xZr Alloys Compared to Three-Phase Fe-30Al-xZr Alloys

The structure and high-temperature mechanical properties of Fe-30 at. pct Al and Fe-25 at. pct Al alloys with various Zr contents are compared. The scanning electron microscope images in chemical contrast mode (R-BSE) as well as EDS, EBSD, and X-ray diffraction were used to determine the structure and phase composition. The as-cast alloys (both Fe-30Al and Fe-25Al) were observed to be two-phase DO₃/B2 + Laves phase λ ₁ (Fe,Al)₂Zr alloys with typical fine lamellar eutectic areas. During the heat treatment of the Fe-25Al alloys, their structure transformed from a DO₃/B2 matrix with fine lamellar eutectic into λ ₁ globular particles situated in a DO₃/B2 matrix. The same structure of Fe-30Al alloys decomposed into three phases: λ ₁ and τ ₁ Zr(Fe,Al)₁₂ particles in a DO₃/B2 matrix. The hardening in both groups of alloys (Fe-25Al and Fe-30Al) due to the presence of Zr-containing λ ₁ and τ ₁ phases is compared.     

Comparison Study of Microstructure and Phase Evolution in Mg-Nd- and Mg-Gd-Based Alloys

Microstructure and phase evolution in Mg-Nd-, Mg-Gd-, and Mg-Gd-Nd-based alloys with additions of Zn, Zr, and Y were analyzed in the as-cast, solution-treated and aged conditions. Close similarity between the as-cast microstructures and precipitation sequence during aging was revealed. Along with this, distinct features of eutectic compounds and of crystal structure, composition, and orientation relationships of β″, β′, and β ₁ phases were established. Formation of Zn₂Zr₃ rods in Mg-Nd-based alloy and cuboid-shaped particles in Mg-Gd- and Mg-Gd-Nd-based alloys is discussed. The features of the age hardening curves were connected with differences between β″ → β′ transformation and different diffusivities of Gd and Nd in Mg-matrix.     

Evolution of Texture and Deformation Mechanisms During Repeated Deformation and Heat Treating Cycles of U-6Nb

The evolution of the crystallographic texture and lattice strain of uranium 6-weight percent niobium alloy samples are tracked during multiple deformation and heat treating cycles in an effort to understand and control the mechanical properties of the material following thermo-mechanical processing. The heavily twinned microstructure and low-symmetry crystal structure of U-6Nb result in multiple sequential active deformation mechanisms associated with distinctive deformation textures in strain ranges from 0-0.15 true strain. It is found that heating into the high-temperature γ-phase erases much of the texture formed during deformation at room temperature in the α′′-phase and resets the active deformation mechanisms. Through a small number of deformation/heat treat cycles to moderate strains, i.e., ~ 0.13 per cycle, the flow strength of the material is recovered to its original value. However, on the fourth such cycle, a reduction of strength is observed and the sample failed.

     

铜合金空洞缺陷形变演化研究探讨*

铜加工材的铸坯内部常存在气孔、缩孔等空洞缺陷,在后续加工过程中,这些空洞缺陷常演变为内部裂纹或表面缺陷,导致成品率降低。在生产过程中,可借助变形和升温来消除铸坯内部的空洞缺陷。空洞的形变闭合是消除缺陷的先决条件,因此有必要开展铜合金中空洞缺陷的形变演化研究。本文对金属空洞缺陷形变演化的研究进展进行了梳理;基于对某锡磷青铜连铸板坯内部空洞缺陷及铸态组织的观察,重点讨论了现有研究成果对于铜合金的适用性,指出了材料微观结构对空洞缺陷形变演化的潜在影响;针对当前研究在几何建模方面的难点,采用Python语言设计了含任意椭球空洞的体元模型自动建模程序。     

Dependence of Deformation Twinning on Grain Orientation and Texture Evolution of High Manganese TWIP Steels at Different Deformation Temperatures

 Mechanical properties, microstructure and texture evolution were studied in two tensile-deformed high manganese TWIP steels at different temperatures. Special attention was paid to the effects of deformation temperature and grain orientation on twinning behavior. The results showed that, at -70 ℃ and at room temperature, both twins and hexagonal martensite were found in a lower manganese steel of 26Mn. With deformation temperature rising, twins became less and they disappeared at 500 ℃. Strong <111> texture appeared at 300 ℃, while it weakened at 500 ℃ due to the low strain rate and higher stacking fault energy. EBSD measurement revealed the dependence of deformation twinning on grain orientation at all test temperatures.     

Effect of Temperature and Composition on NiAl Precipitation and Morphology in Fe-Ni-Al Alloys

NiAl-strengthened ferritic alloys have been of particular interest because of their possibilities as a high-temperature material for power-generation purposes. In the present work, the effect of temperature and composition on the precipitation of the NiAl (β′) phase was studied using a diffusion couple made of alloys Fe_0.50Ni_0.25Al_0.25 and Fe_0.80Ni_0.08Al_0.12. The composition gradient was obtained with a diffusion annealing treatment at 1373 K (1100°C), and the precipitation was promoted by aging at 1123 K, 1173 K and 1223 K (850 °C, 900 °C and 950 °C) for 5 hours. The formation of a supersaturated solid solution and the precipitation of the β′ phase were obtained after the diffusion annealing and aging treatments, respectively. A gradual increase in the size and volumetric fraction of the precipitates was evident in compositions with higher NiAl. This promoted changes in the precipitate morphology that followed the sequence: rounded cuboids → plates → irregular (maze-like). Compositions with a low β′ volumetric fraction followed the predicted size distributions of the Lifshitz-Slyozov-Wagner (LSW) theory. Finally, it was observed that the hardness tends to increase inversely to the Fe content and decreases only because of precipitate coarsening. The achieved results provide new information regarding the dependency of the morphology of β′ precipitates with composition and temperature.     

Heterogeneous Phase Transformation Texture Evolution in Low Alloyed ULC Steel Sheets

In the present study the cold rolled sheet of ultra low carbon steel alloyed with manganese and aluminium has been investigated after α ? γ ? α transformation annealing in vacuum. The texture analysis was carried out on the surface, sub‐surface and in the bulk of the annealed sheet. A <100> // ND and <110>//ND texture with weak intensity is observed on the sheet surface and a strong <111>//ND fibre in the bulk of the transformed sheet. In depth micro‐texture analysis by orientation contrast microscopy reveals that two different types of orientation selection mechanisms could be active. The texture at the metal‐vapour interface is controlled by surface energy anisotropy (producing a local <100>, <110>//ND texture at the surface) and a texture memory mechanism generating strong <111>//ND fibre is active in the bulk of the sheets.